Final12

MANUFACTURING AND SYSTEM DESIGN OF INSULATION FOR AIR COOLED TURBO GENERATOR BY V.P.I PROCESS

PREFACE 





Power is the basic necessity for economic development of a country. production of electrical energy its per capital consumption deemed as an index of standard of living. An AC generator works on the principle of ‘Electro Magnetic Induction’.

INTRODUCTION 





Turbo generators are machines which can generate high voltages and capable of delivering KA of currents The designer should be cautious in designing the winding insulation. Insulation design plays a major role on the life of the Turbo Generator



First half we discuss about manufacture of a



The latter half we explain the insulation design



We more over stress on stator manufacture and on VPI Process

STATOR MANUFACTURE PROCESS:



Stator core construction and



Coil construction and their assembly.

Stator core construction PREPARATION OF STATOR LAMINATIONS  RECEPTION OF SILICON STEEL ROLLS  SHEARING- cutting

BLANKING AND NOTCHING







   

Deburring: Carried out for individual laminations to remove extra projection material -5 μicrons Varnishing: Sheets are dried at a temperature of around 300 – 400 oC 8-10 microns, mini tester, 90 secs Quality Check: viscosity of varnish using DIN 4 cup, should empty in 44 secs xylol test-varnish should not dissolve Mandrel- no cracks Hardness – 7H pencil I.R – 20 laminatons ,26 KG/CM ,IR should be 2

greater than 1MΩ

STATOR CORE ASSEMBLY A.TRAIL PACKET ASSEMBLY B. NORMAL CORE ASSEMBLY i) Trail packet assembly ii) Normal packet assembly  In process pressings 150 kg/cm2  Fitting of clamping bolts  Guide bars, winding brackets

MANUFACTURE OF STATOR COILS

STATOR WINDING INSULATION SYSTEM FEATURES 

Strand Insulation     

For roebel and multi turn coils Easy to bend Skin effect-greater R Skin effect of cu 8.5mm at 60hz Damage during insulation.







Turn Insulation  Shorts b/w turns  100 turns 2ndary of auto t/f  100 times rated Ground wall Insulation  Triggers ground fault relay  If close to neutral- special III harmonic GF relays Slot discharges  Ground V at slots n almost cond pot in OH.  SD takes place if voltage gradient at the transition from slots to the OH is excessive.

A) For Resin Rich Process  

Reception of copper conductors Transposition

Resin Rich Process Contd…, 

Putty operation   



Stack consolidation 



775 varnish_ and mica putty on width faces Mica putty 775varnish+powder+chinaclay 2 to 3 bars at 150kg/cm2 --- 140-160o for 3hrs

Bending    

1-2-OH-3 BEND on BS NOMEX upto 3bend Heated 600 for 30 mins IH and IS tests

R.R process Contd…, 

Final taping 



12 ½ in SP and 9 in overlap.

Intermittant layers      

ICP – By butting only in SP Split mica – 1 layer + cond taping without overlaping OCP – only in SP ECP – end of SP to OH 90 TO 110mm. Hyper seal tape – end of SP to 3rd bend with over lapping – anti-fingering IH and IS tests

RR process Contd…, 

Final baking    



1 hr 90o jelling 30 min 110o + tightening 90- 110 25% remains Raise to 165 for 3 hrs

Conductive on SP and S.C from end of SP to 3rd bend. 

HV and tan tests

DISADVANTAGES OF RESIN RICH SYSTEM OF INSULATION   



Resin is a costliest material. It is a very long procedure Due to fully manual oriented process, the cost is more It is possible to process stator bars only.

B. Resin Poor Process 

Putty operation 

 



Nomex sheets in the cross overs Form mica net Wrapped with PTFE.

Final taping 

9 ½ in SP upto OH and 6 ½ in Intermittant Layers

10.1 ADVANTAGES OF RESIN POOR SYSTEM OF INSULATION 

It has better dielectric strength



Heat transfer coefficient is much better



It gives better capacitance resulting in less dielectric losses due to which the insulation life will be more



The cost will be less and it is latest technology



Reduction in time cycle and consumption for MW also less and it gives high quality

RESIN POOR SYSTEM

1. The insulation tape used in this system has 40% resin. 2. This method follows thermosetting process. 3. There is a need for addition of resin from outside. 4. Reduction in time cycle for this process 1. No tests are carried out while at processing 2. Processing of bars along with stator and with conductors and processing of exciter Coils along with exciter is possible. 3. The cost of repair is more 4. The overall cost is less compared to resin rich system.

RESIN RICH SYSTEM

1. The insulation tape used in this is 7% of 40% resin. 2. Same as in resin poor. 1. Further addition of resin is not required from outside. 2. It is very long process and time consuming while at processing stage. 3. Tests are being carried out Stage. 1. Processing of stator bars is only possible in resin rich systems. 2. Repairing work is easy. 3. The total cost in this process is more.

Stator Winding 

The most prime part of a winding is insulation

ASSEMBLY OF STATOR

Winding holder’s assembly

WINDING HOLDER ASSEMBLY  





Adapt required design size HGL rings on both sides centre with respect to core Individual for pressing fixture apply pressure 60 KG/CM2 for 30 min Tie with neoprene glass sleeve

   





Check for uniform gap in overhang Top bar matching with bottom bar pitch Use RTD Inserting glass mats ,after tie with neoprene glass sleeve EYE FORMATION : Brazing the conductors with silver foil Adv : circulating current losses

Connecting rings assembly Phase connectors



CONNECTOR RINGS: Connect all the connectors to the phase grooves ,by jointing with slaver foils ,insert nomex and tape with semica folium



RTDS are kept in straight portion

PHASE CONNECTORS : Consist of flat copper sections ,low specific current loading

THE VPI PROCESS

INTRODUCTION TO VACUUM PRESSURE IMPREGNATION SYSTEM -DR MEYER WESTING HOUSE house earlier VPI SYSTEM -Bitumen Bonded Mica Flake Tape  Drawback -thermal limitations  Failure of TG in 1970’s 



Failures were due to two types of problems: -Tape separation -Excessive relaxation of the main ground insulation

New improved VPI system -uses resin and mica improved mechanical ---strength and electrical properties Advantages of increase in life more economical

Vacuum Pressure Impregnation of resin poor insulated jobs 

Preheating: the completed stator for period of 1 hr at 60 deg , temp>85deg



Lifting and shifting



Vacuum cycle: vacuum pressure of about 0.2 mb is maintained for about 17 HRS Vacuum drop test





Heating the resin

  

  

Resin admission. Resin settling Pressure cycle: subject resin to pressure cycle of 4 kg/ cm2 of dry nitrogen, subj for 2 hrs. Aeration Post curing cycle Cleaning

FACILITIES AVAILABLE IN VPI PLANT IN BHEL 

Steam furnace for preheating      

Size of chamber: 2 * 2 * 6.5 M Maximum temperature: 160°C Electrical power consumption: 75KW Work place: 1425 Work centre: 3215 Stream inlet: 200-250°C

DATA COLLECTION OF SAMPLES

Date and time

RTD-I(°C)

RTD-II(°C)

Furnace air temperature

Remarks Rotor temperature is reached to 60± 3°C at 2:00hrs on 31.5.2007 and it is maintained for 4 hrs i.e., up to 6:00 on 31.5.2007

30.5.2007

19:00

32.0

30.0

45.6

30.5.2007

20:00

45.4

48.6

57.9

30.5.2007

21:00

49.9

50.9

63.4

30.5.2007

22:00

52.5

54.3

70.5

30.5.2007

23:00

53.3

55.1

73.4

30.5.2007

24:00

56.6

57.3

75.6

31.5.2007

1:00

59.9

60.2

75.1

31.5.2007

2:00

62.4

63.9

77.0

31.5.2007

3:00

62.3

64.7

77.0

Rotor is switched to vac 140 tank at 7:00 hrs on 31.5.2007

31.5.2007

4:00

63.3

64.1

75.0

31.5.2007

5:00

63.3

64.0

75.6

31.5.2007

6:00

63.1

63.7

75.6

Date and Time

Vacuum in graph Vacuum in (mbar) meter (mbar)

Job temperature (°C)

Resin cycle

8.5.2007

22:00

--

--

54.37

Resin tanks 025,102 are heated for impregnation

8.5.2007

0:00

--

--

54.89

Viscosity of resin at 60°C is 33CP

9.5.2007

2:00

--

--

59.02

Viscosity after aging is 36.10CP

9.5.2007

3:30

0.65

0.65

61.6

9.5.2007 and 10.5.2007

9.5.2007

5:30

0.41

0.40

63.59

Resin admission started at 19:45hrs

9.5.2007

7:30

0.28

0.29

64.2

Resin admission completed at 19:55hrs

9.5.2007

9:30

0.22

0.22

63.2

Pressurisation started at 20:00hrs

10.5.2007 22:30hrs

144.4

151.3

143.7

145.1

144.1

35.9

11.5.2007 1:30hrs

143.1

146.7

145.2

145.1

145.2

33.8

11.5.2007 4:30hrs

144.3

151.0

143.6

144.0

144.7

31.1

11.5.2007 7:30hrs

135.7

142.1

144.3

145.1

145.0

31.3

11.5.2007 10:30hrs

135.0

135.7

135.1

135.0

135.8

34.8

11.5.2007 13:30hrs

135.6

141.4

135.4

135.6

135.9

38.3

11.5.2007 17:30hrs

148.0

149.2

142.8

142.2

142.1

39.8

Job temp. is reached to 140± 5°C i.e., from 136.2°C to 145.6°C at 9:30hrs on 10.5.2007 and it is maintained for 32hrs i.e. up to 17:30hrs on 11.5.2007.

Furnace is switched off at 17:30hrs on 11.5.2007 and circulation fans kept running till the job temperature is reached from 70°C- 75°C

JUSTIFICATION  

Justification can be done by two tests HV and TAN δ tests

PRESENT INSULATION SYSTEMS IN THE WORLD 

 



Vacuum pressure impregnation (VPI) of individual coils and bars Global VPI of complete stators Hydraulic molding of individual coils and bars using resin-rich tapes Press curing of individual coils and bars, also using resin-rich tapes



Westinghouse Electric Co.: Thermalastic™



General Electric Co. :Micapals I anII™,EpoxyMica Mat™, Micapal HT™, and hydromat™ Alsthom, GEC Alsthom, Alstom Power: Isotenax™, Resitherm™,



Siemens AG, KWU: Micalastic™ 

ABB Industrie AG: Micadur™,



Toshiba Corporation: Tosrich™ and Tostight- I™



Mitsubishi Electric Corporation



Hitachi, Ltd.: Hi-Resin™, Hi-Mold™, and Super Hi-Resin™



Summary of Present-Day Insulation Systems

A NEW hype IN INSULATION SYSTEM MICALASTIC









Trademark for Siemens insulation systems for high-voltage windings Mica, capable of withstanding high electrical and thermal loads, Most important criterion ability to durably withstand partial electrical discharges

MICALASTIC IN I’TAIPU 

1. 2.

3. 4.

Manufacturing and design Single coils are continuously wrapped with MICA tape Then dried out and degassed in a vacuum impregnation tank Nitrogen pressure applied to the impregnating bath Curing

Features 



 

U-shaped slot liners of polyester fleece impregnated with a conductive material, and a conductive, curable synthetic resin paste between the surface of the bar insulation and the slot liner Bracing the end windings and jumpers by using glass fiber reinforced spacers and epoxy-resin impregnated Mechanical stiffness commissioned in 1958, and are still in operation today

Fitting of Roebel Bars into Slots



None of the MICALASTIC stator windings showed evidence of damage or slot discharges



Practically un limited service life outstanding insulating properties,



The MICALASTIC insulation regarded as the standard for the reliability of rotating electrical machines



Curable synthetic resins with a much higher long-term resistance to high temperatures by VPI



Not technically or economically a viable prospect due to their conservative thermal design.

CONCLUSION: 



Vacuum Pressure Impregnation (VPI) yields superior results with better insulating properties, Advancements are possible by including MICALASTIC INSULATION used in HYDRO PLANTS

Any Queries..???

Thank you